1. Field of the Invention
The present invention relates to a process for the vapor deposition of a semiconductor of a compound of elements of the groups III.V, in which a semiconductor of a compound of elements of the groups III.V having an improved electron mobility can be formed on a substrate of a single crystal of alumina by the metal-organic chemical vapor deposition. Furthermore, the present invention relates to a semiconductor element having an improved surface smoothness in a semiconductor layer, which is prepared according to the above-mentioned process.
2. Description of the Prior Art
The technique of utilizing a semiconductor of a compound of elements of the groups III.V for a light-emitting element or light-receiving element has recently been markedly developed, and for example, the technique of forming a semiconductor of a compound of elements of the groups III.V, such as GaAs, on a single crystal substrate by the gas phase epitaxial growth has attracted attention. In the case where a substrate of a single crystal of alumina is used, an advantage is attained in that a high transmission of rays having a wavelength of 0.2 to 5 .mu.m is obtained, and therefore, application of this semiconductor to various devices is expected. For example, when this semiconductor is used for LED, emission of light from the substrate side is possible, and when the semiconductor is used for a photoelectric conversion device, receipt of light on the side of the substrate is possible.
As means satisfying this demand, there has already been proposed the metal-organic chemical deposition method (ordinarily called "MOCVD method") for forming a GaAs film on a substrate of a single crystal of alumina (Journal of Applied Physics, Vol. 42, No. 6 (1971), page 2519).
More specifically, according to this proposal, a GaAs film is epitaxially grown on a substrate of a single crystal of alumina by the chemical vapor deposition (CVD) method using trimethyl gallium (Ga(CH.sub.3).sub.3) as an organic metal gas and arsine (AsH.sub.3) as a reactive gas.
According to this process, however, many lattice defects are formed in the interface between the alumina single crystal substrate and the GaAs single crystal film, and therefore, a film thickness larger than 20 .mu.m is necessary for obtaining a high electron mobility, and improvement of the crystallinity of this film is desired.
Furthermore, according to the conventional process, convexities and concavities are readily formed on the surface of the GaAs film, and the light emission efficiency is drastically reduced in the light-emitting element comprising this semiconductor. When this semiconductor is used for an element of a transistor or IC, fine processing is impossible. Accordingly, utilization of these film devices is inhindered.
Therefore, development of a semiconductor of a compound of elements of the groups III V having a smooth surface is desired, but formation of a semiconductor of a compound of elements of the groups III.V having a smooth surface on a substrate of a single crystal of alumina has not been reported.